The present invention relates to an apparatus for supplying or feeding fuel to a motor vehicle engine from a fuel tank. The invention also relates to a method for improving the reliability of operation of the apparatus for feeding fuel.
An apparatus for feeding fuel of this type is known and includes a pump portion and a direct current-drive motor through which fuel flows mounted in a housing part, which is provided with a commutator device, which has a collector, on whose sliding surface commutator brushes, which are part of the operating circuit of the drive motor, are pressed during operation of the drive motor by brush contact springs made from electrically conductive material.
So that this known fuel feed apparatus (DE-OS 30 16 086) can also be used for feeding a medium which acts like an electrolyte, the individual wires of copper conductor leading from the electrical terminals to the carbon brushes located in a box or pot-like housing or guide are enclosed in a protective jacket made from Nickel, Zinc, Silver or Aluminum. This is because in the alcohol fuel currently under consideration, which contains for example 15% methanol (M 15), the electrical conductivity is in the Micro-Siemens Region (uS). This is based on the fact that methanol combines with water. Pure methanol (M 100) or ethanol (E 100) fuel increases its conductivity, because of oxidation susceptibility and with it formation of formic acid (in M 100) and/or formation of acetic acid (in E 100). In regard to electrical conductivity in the Micro-Siemens Region, these fluids already act as electrolytes so that because of the potential differences in the electric motor a deposit occurs, particularly on the bare conductors which are exposed to the flowing fuel on the anode side.
With the conventional fuel, whose conductivity is in the Pico-Siemens Region (ps), these considerations play no roll. The features known from the above-mentioned state of the art for preventing the mentioned electroerosion stiffen the brush wires so much that the proper contact of the brushes on the contact surface of the commutator is no longer guaranteed under action of the conventional brush contact springs formed as coil springs. However a compensating stiffening of the contact springs increases the wear on the carbon brushes and lowers the efficiency of the electrical drive motor and thus also the fuel feed unit. Further background of the problems are described in DE-OS 30 16 086. Express reference is made to this publication so that the disclosure of that publication can be considered as part of the disclosure of this application.